Make sure track path is saved to track view so sending it back won't crash. Keep track of users for requests to implement limited amounts of requests. Implement requesting with limits.

src/GroovePlayer.h

@@ -65,7 +65,7 @@ public:
         User userInvolved;
         std::list<AudioTrack> tracksInvolved;
     };
-    std::list<AudioTrack> requestQueue;
+    std::list<std::pair<AudioTrack,User>> requestQueue;
     std::list<PlayerEvent> lastInternalEvents;
     Wt::Dbo::backend::Sqlite3* sqliteConnection;
     Wt::Dbo::FixedSqlConnectionPool* connectionPool;